It is known to provide water pumps on stationary or vehicular engines in order to circulate coolant through the engine in order to prevent the engine from overheating. In many applications, the water pump is driven by a belt or the like that is itself driven by a crankshaft of the engine. As a result, the speed of the water pump is determined by the speed of the engine. The coolant flow of the water pump is generally selected so that in the worst case combination of engine speed and cooling needs, the engine will be sufficiently cooled by the coolant flow from the water pump. However, inherent in such a design practice is that that water pump is pumping more coolant than necessary in some situations.
It would be advantageous to be able to provide a water pump or a pump in general that had some means of reducing coolant flow when it is not needed.